1. Field of the Invention
The present invention relates to a navigation system, and in particular to a system that uses traffic information to provide route guidance for vehicles.
2. Description of the Related Art
Japanese Patent Application Laid-Open (Kokai) No. 2000-76580 describes a traffic information distribution device for sending predicted traffic information to a user terminal in response to a request from the user. The patent document discloses a technique in which the traffic information distribution device determines and then sends to the user terminal, predicted information to be sent to the user terminal based on the road information sent from the user which traffic status the user is interested in knowing, and on the time which predicted information the user requires.
However, the technique according to the patent document has a disadvantage in that a user terminal download a large amount of information from the traffic information distribution device irrespective of whether the user will actually use the data. In light of this problem, the present invention aim to provide a technique for more efficiently downloading traffic information in a navigation system comprising a server for distributing traffic information and a terminal unit.